Spammers are leveraging more and more armies of infected PCs to deliver malicious content. These infected PCs are often referred to as botnets. The term botnet generally refers to a group of infected processors (commonly referred to as zombie computers) executing and/or spreading malicious software (spam), such as viruses, worms, Trojan horses, and the like. Typically, the owner or user of a zombie computer does not known it is infected and a source of spam. Lists of known sources of spam can be found on a variety of block lists. A block list can be utilized to refuse to receive email and the like from IP (Internet protocol) sources on the list. The generation of block lists however, is gradual and slow, and thus does not provide a mechanism for quickly discovering sources of spam. At any point in time, it is estimated that less than 9% of existing botnet sources are listed on a block list.